Car face wall architecture for a car such as a train car made from sandwich composite material

ABSTRACT

A car belonging to a rolling vehicle, characterized in that it includes sidewalls in the form of a single piece made from composite material including a sandwich structure provided with a first skin on the outside of the car, a second skin on the inside of the car and a closed-cell foam or honeycomb core between the skins, the walls being provided with window openings formed by interruptions in the drapes of longitudinal fibres, transverse fibres and intersecting diagonal fibres, the openings having a polygonal shape that reduces the surface area of interrupted diagonal fibres in the corners of the openings.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/EP2015/073863, having an International Filing Date of 15 Oct. 2015,which designates the United States of America, and which InternationalApplication was published under PCT Article 21(2) as WO Publication No.2016/059147 A1, and which claims priority from and the benefit of FrenchApplication No. 1460011, filed 17 Oct. 2014, the disclosures of whichare incorporated herein by reference in their entireties.

BACKGROUND

1. Field

The presently disclosed embodiment concerns a car face wall architecturesuch as a train car made from sandwich composite material equipped withopenings.

The disclosed embodiment relates to a design solution for a structuralpanel made of composite material equipped with openings, i.e. bays,hatches, windows which are designed to lighten globally the weight ofthe structure, and are applicable in particular for the walls of arailway transport body, whether this involves urban rolling stock orstock for a subway, tramway, regional train or cars for high-speedlines.

2. Brief Description of Related Developments

The designers of train structures must obtain compromises betweenvarious requirements which are sometimes contradictory, i.e.:

They attempt to decrease the weight of the structures in order toincrease the useful load and/or to reduce the energy consumption, butthey must control the production costs, and therefore find simplesolutions, whilst ensuring the comfort and safety of the passengers, andin particular, in a non-limiting manner:

-   -   By limiting the structural deformations of the train cars, which        involves sufficient flexural rigidity of these cars. This        rigidity is also important in order to avoid coupling with the        suspension modes of the trains;    -   By limiting the noise inside the cars;    -   By ensuring that the passengers are protected against fire and        fumes;    -   By withstanding the pressure waves;    -   By withstanding the traction and compression associated with the        traction.

More specifically, a train body structure acts mechanically like acaisson subjected to flexion, the top (the roof) and the chassis (thefloor) of which constitute the bearing surfaces, and the faces of whichconstitute the vertical shells.

As represented in FIG. 1, the faces for their part are mostly subjectedto shearing stresses 201.

In addition, the panels are also subjected to flexion stresses inducedby the pressure waves of approximately 8000 Pa sustained when ahigh-speed train crosses another and/or passes into a tunnel, as well asto the effect of the vertical loads 201, the weight of the equipment andpassengers on the chassis, and local forces or the like.

Hitherto, the bodies have been substantially constituted by metalstructures, for example mechanically welded aluminum profiles or steelplates, as described for example in document EP0392828A1 orJP2000264200A.

In general, it is found that these structures are, as in documentJP4427273B2, in the form of sandwich walls, i.e. two metal skins whichare connected to one another by elements, or of panels which arereinforced by strengtheners as described in document JP2000264200A, orby a combination of two types of solutions.

However, it is natural in the field of transport to envisage lightersolutions, using high-performance composite materials, as may have beenthe case in the past in the pioneering fields of aeronautics and space.This has been proposed for example in documents EP0544473A1 andEP0544498A1 in the form of sandwich panels with a honeycomb core andstrengtheners inserted.

The need for longitudinal flexural rigidity of the lateral panels isderived from the fact that a train structure is a beam which issupported on its axles. This rigidity must be controlled firstly inorder to limit the flexion, but also to control the vibration andresonance associated with the speed of travel of the trains.

In addition to the problem of the rigidity, it should be noted thatthere are two patents which show the difficulties of controlling thisrigidity because of the presence of windows, i.e. document JP2000264200Awhich proposes strengtheners which are not simply vertical, but theangle of which relative to the vertical is also optimized. This patenteven proposes a continuous window, which is simply concealed locally byinclined floor-to-ceiling connection pillars.

Document U.S. Pat. No. 8,656,841B1 proposes windows which are oblong andnot rectangular as usual, and in both cases the form of the window ismodified in order to be compatible with control of the rigidity of thepanels.

The composite structural materials which make it possible to ensure thesaving of weight sought, together with the required level ofperformance, are based on continuous long carbon or glass fibers. Inthis type of material, the fiber represents approximately 50% to 60% ofthe volume, the remainder being constituted by an organic matrix (ingeneral a resin of the epoxy type, but also sometimes polyester, vinylester, etc., and optionally thermoplastic resins such as polyamides,peeks, etc.).

For the production of structures, there are two main families ofcomposite materials:

-   -   So-called monolithic materials, constituted by a stack of        fibers;    -   Sandwich materials, constituted by two skins with a nature        identical to the monolithic materials, separated by a core. This        core is often constituted by a very low-density material of the        honeycomb or foam type or the like (sometimes balsa). This makes        it possible to obtain the required off-plan flexural inertia        properties. This type of structure is advantageous in terms of        performance and cost.

In a sandwich material, the flexural inertia of the panels in thedirection of their thickness is provided naturally by the spacing of theskins. This is one of the major advantages of this type of architecture.

Other core materials can be used, for example denser materials which aredesigned to provide the sandwich structure with sound-absorptioncapacities, see for example document JP2001278039A.

The composite materials thus make it possible to implement the sametechnical solutions as the metal materials, i.e. strengthened monolithicstructures or sandwich structures, but with a wide variety of possiblesolutions, since many combinations are possible between the variousfibers (carbon, glass, SiC, vegetable fibers, etc.), resins (epoxy,polyester, vinyl ester, peek, polyamides, thermosetting orthermoplastic), and the cores (metal honeycombs, foams or the like).

In addition, since the optimum mechanical properties of the compositematerials are ensured by the fibers, these materials are by natureanisotropic, and consequently their optimization of the structures needsthe orientations of the fibers in the thickness of the material to bedefined according to the mechanical stresses to which the structure issubjected.

Thus, for the roof and the chassis, the rigidity requirements lead toorientation of the fibers preferably in the direction of the length. Onthe other hand, as far as the face panels are concerned the shearingstress which is applied must be absorbed by fibers which are orientedrather at + and −45°. It is in fact in these conditions that themechanical functioning of the structure is optimized, and thusconsequently its weight and cost.

Like any vehicle which is destined for passenger transport (motor cars,motor coaches, trains, aircraft, and even space vehicles), train carsmust comprise windows. Since these windows are made from materials whichare different from the remainder of the structure of the vehicle, theymust form the basis of a specific design.

A device for securing the windows to the remainder of the wall or thestructure must be put into place, as for example in patent FR 2911112A1relating to aircraft. In addition, the structure in the vicinity of thewindows must be reinforced as described in US Publication No.2012/0223187A1.

In the case of cars consisting of structures made of composite materialsas previously described, the shearing stress which is applied to theface must be absorbed by fibers oriented at +45° and −45° relative tothe horizontal.

However, as represented in FIG. 3, at the panels of the faces, thepresence of the angles of conventional bays with a rectangular formleads to cutting of the fibers between the top and the bottom of theface panel, which may make it necessary to increase the distance betweentwo windows, or the local thickness of materials between two windows,which complicates the production of the panel and makes it more costly.

Thus, it has been proposed to modify the form of the windows in the caseof a structure made of composite materials, and document US PublicationNo. 2012/0223187A1 thus proposes in this case hatches in the form of a“diamond” for an aircraft fuselage, as well as the manner ofestablishing their dimensions. This form of hatch with a small size isobviously unsuitable for a passenger train.

SUMMARY

It is thus known to produce train bodies made of composite materials, inparticular in the form of sandwich panels.

This being the case, numerous technologies can be envisaged, both interms of materials (fibers, resins, cores) and of methods ofimplementation (draping of pre-impregnated products, infiltration andits variants, etc.). It is also then known to adapt the form of thewindows in order to improve the longitudinal rigidity of the body, andfor aircraft a form of the diamond type has been proposed for thehatches, such as to adapt them even better to the preferred orientationsof the fibers, which involves the optimization of composite materials.The same also applies to the modification of the skins of the sandwichcomposite materials, in order to improve their capacity to withstandmore forces locally.

On the other hand, it is not known to optimize the windows of cars madeof composite material, and the same applies to the manner of production.

However, train windows are distinguished from those of aircraft by theirunit surface, which is significantly larger than that of aircraft, bytheir geometry, which is characterized by elongation (ratio of the highlength relative to the square on the surface, i.e. more than 2 for mostwindows of a body), and by the total glazed surface compared with thewall surface of the lateral structure, which is also very much greaterthan that of aircraft. These aspects are justified by the need toprovide the passengers with maximum comfort during the journey, withvisibility and light being important aspects of this comfort.

Apart from these distinctions, the dimensions of the main part of asection of train body are also distinguished from those of an aircraftfuselage by the following specific features:

-   -   lack of stress caused by the need for static pressurization of        the structure, but on the other hand pressure stresses in the        form of excess pressure waves followed by low pressure affecting        the structure and the bays with rapid dynamics when passing into        tunnels and/or crossing other trains. The levels of these        pressures (peak values) are approximately ±5000 to ±, 6000 Pa,        up to 8000 Pa for high-speed;    -   the need to control the structure's own frequency, in order to        prevent it starting to resonate when the car is travelling,        typically at >11 Hz;    -   the need to withstand the forces (traction/compression) of the        traction between cars.

Finally, and although costs must be taken into account in all industrialactivities, the demands in the field of railways in terms of costreductions are even more stringent than in aeronautics (the cost per kgaccepted is more than 10 times less), which makes this an even moreimportant criterion for the selection of solutions.

The objective of the disclosed embodiment is thus to propose a solutionto reduce the weight of the structures of a train body by use ofcomposite materials, whilst maximizing the glazed surface available forthe passengers.

The disclosed embodiment makes it possible to design a face (wall) of acar made of composite material in the form of a sandwich in a singlepiece, reinforced locally only for the interfaces, based substantiallyon high-strength carbon fibers, sampled in order to optimize themechanical stresses as well as possible, but also taking into accountrequirements of finishing and integration, and comprising openings witha form suitable for better use of this sampling.

More particularly, the disclosed embodiment proposes a rolling vehiclecar comprising lateral walls in a single piece made of compositematerial comprising a sandwich structure provided with a first skin onthe outer side of the car, a second skin on the inner side of the car,and a closed-cell foam or honeycomb core between said skins, said wallsbeing provided with window openings formed by interruptions of drapingof longitudinal fibers, transverse fibers and crossed diagonal fibers,said openings having a polygonal form which reduces the surface ofdiagonal fibers interrupted in the corners of the openings.

In particular, the disclosed embodiment makes it possible to dispensewith strengtheners or metal lattice elements in order to reinforce thestructure.

For increased rigidity of the body, the openings preferably have agenerally hexagonal or octagonal form comprising two large horizontalsides connected by convex lateral borders comprising two segments, threesegments, or one segment with an oval form.

Advantageously, the openings are equipped with a reinforcement borderprovided with a tubular frame.

According to a particular aspect of the disclosed embodiment, thereinforcement border comprises an inner wing for securing of the borderon the edge of the opening on the inner side of the wall.

The tubular frame advantageously has a rectangular cross-section, withthe inner wing extending a face of the tubular frame on the interior ofthe wall.

The inner wing is preferably secured on the interior of the wall bymeans of screws, rivets or other securing means which render the wingand the inner skin of the composite panel integral.

Advantageously, a face of the tubular frame which faces toward theinterior of the car is secured by means of screws, rivets or othersecuring means on a rim of the opening formed by the second skinprojecting from the core of the wall.

According to a particular aspect of the disclosed embodiment, thereinforcement border comprises an inner collar which receives afastening of a window.

According to a particular aspect of the disclosed embodiment, at leastone of the two skins of the sandwich structure is produced by means ofplies oriented in four preferred directions, i.e. 0° (longitudinal axisof the body), 90°, +45° and −45°.

According to an advantageous aspect of the disclosed embodiment, theplies are plies impregnated with unit gsm substance of between 125 g/m²and 500 g/m².

According to an advantageous aspect of the disclosed embodiment whichlimits the number of interrupted plies, the angle segments of saidopenings are inclined between 45° and 60° relative to a longitudinaldirection of the wall, and are preferably inclined between 45° and 50°relative to a longitudinal direction L of the wall.

The threads at 45° are advantageously in the form of at least two ±45°plies made of carbon fiber.

According to a preferred aspect of the disclosed embodiment, the core ofthe sandwich is made of a material selected from amongst polyethyleneterephthalate (PET), polymethacrylimide (PMI), polyetherimide (PEI), analuminum honeycomb or a poly(m-phenyleneisophthalamide) (MPD-I)honeycomb (structure impregnated with phenolic resin).

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the presently disclosedembodiment will become apparent from reading the following descriptionof a non-limiting aspect of the disclosed embodiment, provided withreference to the drawings which represent the following:

FIG. 1 is a skeleton diagram of the shearing stresses according to thelongitudinal direction of a lateral panel of a train car;

FIG. 2 is a detail of a panel according to the disclosed embodiment;

FIG. 3 is a representation of a panel according to the prior art;

FIG. 4 is a view in perspective of part of a panel and openingsaccording to the disclosed embodiment;

FIGS. 5A, 5B are a detail in cross-section of a reinforcement frame at awindow opening in the wall according to two embodiments;

FIG. 6 is a front view of an aspect of a panel according to thedisclosed embodiment for a double-decker car;

FIG. 7 is a schematic representation of the structure of the wallaccording to the disclosed embodiment between window openings;

FIG. 8 is a view in perspective of a car body with walls according to anaspect of the disclosed embodiment;

FIG. 9A is a schematic view of passages of fibers inclined betweenopenings;

FIGS. 9B and 9C are curves representative of the stresses and shearingat the cut-out of the openings within the context of the disclosedembodiment.

DETAILED DESCRIPTION

The disclosed embodiment is described mainly in FIGS. 2 and 4 to 8.

Its principle is to provide a train car 1, an example of which is givenin FIG. 8, comprising lateral walls 2 in a single piece made ofcomposite material.

The material selected has a sandwich structure 10 shown in FIG. 2,provided with a first skin 11 on the outer side of the car, a secondskin 12 on the inner side of the car, and a core made of closed cells 13a or honeycomb 13 b between said skins.

According to the disclosed embodiment, the walls are provided withwindow openings 20 formed by interruptions of drapes of longitudinalfibers, transverse fibers and crossed diagonal fibers 100 of thesandwich structure, said openings 20 as represented in FIG. 4 having ahexagonal form comprising two large horizontal sides and lateral walls29 with a profile in the form of a convex “V” or an oval profile whichreduce the surface of diagonal fibers 100 interrupted in the corners ofthe opening, and represented in FIG. 7 having an octagonal form forwhich the lateral sides comprise three segments.

In comparison with a monolithic structure equipped with a strengthener,sandwich structures provide the following advantages in particular:

-   -   Reduced production costs and weight, thermal insulation function        provided by the core.

Compared with a sandwich structure solution of this type, monolithicpanels have the following disadvantages:

-   -   Higher production cost (assembly of the frames and strengtheners        on the skins), high assembly cost (local assembly in the frame        areas);    -   In addition, the frames are thicker than the sandwich, which        reduces locally the inner volume of the structures constructed.

The materials, i.e. the composite material and core, of the panel, mustbe selected to comply with many constraints, which leads to eliminationof numerous potential solutions and ultimately to selection of solutionswhich are once again compromises from amongst the multiple solutionsenvisaged.

The main constraints to be taken into account are described below,firstly in relation to the mechanical constraints.

For the skins:

-   -   The traction/compression modules of the elementary plies, an        elementary ply being the basic element of the stacks of fibers,        either a single-layer one-way sheet UD or a fabric, must provide        the required rigidity in the stack. In this case, the choice of        fiber is of primary importance. For reasons of cost, the choice        has been for industrial strength “HR” (high resistance) fibers,        in particular T700 made by the company Hexcel, TR50S made by        Mitsubishi, or Pannex 35 made by Zoltec;    -   The mechanical strength of the elementary ply under the service        loads must be verified. The properties of the resin are just as        important as the properties of the fiber.

Taking into account the structural application concerned and thestringent constraints with which the material must comply (service lifeof 30 years in a humid environment, temperature resistance >60° C.,cycle fatigue up to 10 million cycles, etc.), resistance to impactsetc., an epoxy resin was selected.

The minimum mechanical properties of the carbon/resin one-way fiber plyconcerned at the end of the service life and at the maximum operatingtemperature are as follows:

Data (max T° end of life) resistance composite material- >726 traction0° (Mpa) composite material modulus- >114 traction 0° (Gpa) resistancecomposite material >508 in compression 0° (Mpa) composite materialmodulus in >103 compression 0° (Gpa) composite material modulus in >3.0traction at 90° (Gpa) plane shearing resistance- >33 Tau_12 (Mpa) planeshearing modulus-G_12 >2.0 (Gpa) ILSS (inter-laminar shearing >29stress) (Mpa)

The minimum mechanical properties of the one-way glass fiber/resin plyconcerned at the end of the service life and at the maximum functioningtemperature are as follows:

Data (max T° end of life) resistance composite material- >472 traction0° (Mpa) composite material modulus-traction >35 0° (Gpa) resistancecomposite material in >331 compression 0° (Mpa) composite materialmodulus in >30 compression 0° (Gpa) composite material modulus intraction >3.0 at 90° (Gpa) plane shearing resistance-Tau_12 >29 (Mpa)plane shearing modulus-G_12 (Gpa) >2.0 ILSS (inter-laminar shearingstress) >21 (Mpa)

For the core of the panel:

-   -   The shearing modulus intervenes in the flexural rigidity of the        panel. The resistance in traction/compression and shearing of        the material must be designed in particular to ensure sufficient        mechanical resistance under the service loads. The density of        the material is an important factor for the purpose of        minimizing the weight of the structure.

In addition to the mechanical performance, the choice of materials ofthe sandwich panel involves other considerations, such as thecompatibility with the production process concerned. The costconstraints associated with the large dimensions of the parts justifythe selection of a production process under vacuum (outside anautoclave). The impact of this choice plays a primary part in theselection of the resin.

Consequently, the core material must be able to withstand theconstraints (pressure=0.1 Mpa+temperature up to 120° C.) induced whenthe polymerization cycle is implemented. These constraints lead toelimination of the use of certain products (e.g.: PET foam with densityof less than 100 kg/m³).

The material must also comply with railway standards for fireresistance, and in particular the 2013 version of standard EN45545.

For cellular foams, certain families of materials such as polyethyleneterephthalate (PET) in certain densities, polymethacrylimide (PMI) andpolyetherimide (PEI) comply with all of these requirements. Cores madeof aluminum honeycomb or poly(m-phenyleneisophthalamide) (MPD-I)honeycomb (structure impregnated with phenolic resin) (known under thebrand name NOMEX for example) also comply with them.

The thermal insulation is also a constraint to be taken into account.Use of a core material constituted by close cells, which intrinsicallyhave excellent thermal insulation properties, provides the advantage ofincorporating the function of thermal protection in the production ofthe panel, and thus saves costs and cycle time for the implementation ofthis function, which is generally carried out on the body structure.

In order to prevent phenomena of accelerated ageing of the materials byabsorption of water, but also risks of deterioration under the effect offrost, in this case also the choice of a closed-cell core material ispreferred.

Taking into account the above points, and including constraints of cost,the solutions which are preferably selected are described within thecontext of an application as follows:

The face of the car is a sandwich panel in a single piece pierced inorder to provide the openings such as windows, doors, display devices orthe like. The openings comprise reinforcements which are used forsecuring of elements on these openings (windows, doors, etc.), and makeit possible to compensate for the loss of rigidity of the face panelassociated with the presence of the hole. This reinforcement at thewindow openings is provided by a reinforcement border with a borderingframe (metal in the case in question) as represented in FIG. 4, and incross-section of the composite panel hole bordered by the reinforcementborder 21 in FIGS. 5A and 5B.

According to these examples, the reinforcement border 21 is providedwith a tubular frame 30.

In the case in FIG. 5A, the border comprises a wing 31 known as theinner wing, which makes it possible to secure the border on the edge 2 aof the opening in the inner face of the panel, i.e. the face which isinside the body.

The tube which forms the tubular frame 30 has a rectangularcross-section, with the inner wing 31 extending a lateral face 21 a ofthe tubular frame of the reinforcement border 21.

The inner wing 31 is secured on the wall on the inner side of the car bymeans of screws, rivets or other securing means 32, which, in the caseof rivets, will grip the outer wing and the skin forming the inner faceof the wall of the car. A seal 37 a is interposed between the wing 31and the inner face of the wall.

The lateral face 21 b of the tubular frame 30 which faces towards theexterior of the car is secured by means of screws, rivets or othersecuring means 32 onto a rim of the opening provided by the skin 2 b ofthe panel which forms the outer face of the body, and projects relativeto the core of the panel. A seal 37 b is interposed between the lateralface 21 b and the second skin 2 b.

The reinforcement border 21 also comprises an inner collar 34 forsecuring of the window.

The inner core 31 is secured on the wall of the inner side of the car bymeans of screws, rivets or other securing means 32, which, in the caseof rivets, will grip the outer wing and the skin forming the inner faceof the wall of the car. A seal 37 a is interposed between the wing 31and the inner face of the wall.

The lateral face 21 b of the tubular frame 30 which faces towards theexterior of the car is secured by means of screws, rivets or othersecuring means 32 onto a rim of the opening provided by the skin 2 b ofthe panel which forms the outer face of the body, and projects relativeto the core of the panel.

The reinforcement border 21 additionally comprises an inner collar 34for securing of the window.

In the case in FIG. 5B, in addition to the elements previouslydescribed, a framing plate 36 is secured on the outer lateral face 21 bof the border and on the panel 2. In this case, the framing plate 36 andthe outer skin end in a bevel in a complementary manner, and thesecuring elements 33 b which render the plate and the panel integral aresecured in the core of the panel.

A seal 37 c is interposed between the plate on one side and the borderand the panel on the other side.

The skins are made of carbon fibers of grade “HR” and glass E accordingto the areas and requirements, and an epoxy resin which, whenimpregnated with the above fibers in a monolithic panel with a thicknessof between 2 and 8 mm, has properties of FST>HL1, R1, R7 (according tostandard EN45545).

The thickness of a skin is from 2 to 5 mm, and the fibers are in theform of one-way sheets or pre-impregnated fabrics.

For the core a PET foam is selected with a density of 100 kg/m³ or more,a PMI foam with a density of 50 kg/m³ or more, or a honeycomb with adensity of kg/m³ or more, depending on the areas and requirements. Thethickness of the core is from 10 mm to 200 mm, in this case alsodepending on the areas and the needs.

The method selected is polymerization under vacuum pocket (outside anautoclave) with a temperature which does not exceed 120° C.

It will be appreciated that the precise thickness of the skins, the coreand the orientations of the fibers in the skins depend on the stresseson the body.

As previously indicated, these specifications relate to the vehicle'sown frequency, which must be more than 10 Hz or so; it is then necessaryto select the values of the face in terms of rigidity,compression/traction forces which are associated with the travel of thecar, and are approximately a hundred tonnes, and the flexure forcesassociated with the pressure waves, of approximately 10,000 Pa.

Globally, for a car which is approximately 15 m between bogeys, thusmaking it possible to transport around 40 passengers in this area, theconventional calculations by means of finite elements result in asandwich material approximately 40 mm thick.

According to one aspect of the disclosed embodiment, in particular for adouble-decker car with lower windows 20 a and upper windows 20 b, thewall will comprise different skin thicknesses between the low part ofthe face and the high part. According to the example given in FIG. 6,the lower part of the panel 301 is produced with a skin thickness of2.78 mm and a core thickness of 38 mm, whereas the upper part 302 isproduced with a skin thickness of 3.33 mm and a core thickness of 38 mm.

It will be noted in particular that each skin has a thickness ofapproximately 3 mm, which incidentally is significantly more than thethickness of aircraft fuselages, which do not exceed 2 mm.

In the main areas (excluding connections and particular points), atleast one and preferably both skins of the sandwich structure areproduced for example using high-strength plies made of pre-impregnatedcarbon, for example of the type T700 made by the company Toray.

In order to produce the skin(s), it is possible to use as basicelements, by way of example: a pre-assembly of plies with fibersoriented at +45°, 0°, −45°, respectively with a dry gsm substance of 125g, 250 g, 125 g, a one-way ply oriented at 0° with a dry gsm substanceof 500 g, and a ply which is a fabric oriented at 0°/90° with a dry gsmsubstance of 500 g, these values being given with a tolerance of ±10%.

The table below describes the fibrous architecture which can resultaccording to the areas of application of the composite material.

Gram 500 500 500 weight of dry fiber (g/m²) Tvf (%) 50.00% 50.00% 50.00%Unit 0.556 0.556 0.556 thickness (mm) density 1500.00 1500.00 1500.00parts Skin thickness and Height of height HT of n × UD n × UD n × (excl.galvanic areas core (mm) panel (mm) stack 0° carb 90′ carb ±45° carbprotection ply) central 10 16.7 n. plies 3 1 2 area roof th (mm) 1.670.56 1.11 3.33 (one skin) % 50% 17% 33% 100.00% Upper 38 44.8 n. plies 22 2 vertical th (mm) 1.11 1.11 1.11 3.33 facade % 33% 33% 33% 100.00%(one skin) Lower 38 43.7 n. plies 2 1 2 vertical th (mm) 1.11 0.56 1.112.78 facade % 40% 20% 40% 100.00% (one skin)

In general, it is found that the optimization of the structure requiresthe presence of fibers at 0°, 90° and ±45°.

The fibers at 45° are particularly suitable for absorbing the shearingforces within the context of the panel concerned.

In this example, the preference is for a 50% distribution of one-wayfibers at 0°, 17% fibers at 90°, and 33% fibers at ±45°, in order toproduce a roof, 33% one-way fibers at 0°, 33% fibers at 90°, and 33%fibers at ±45° for an upper vertical facade, and 40% one-way fibers at0°, 20% fibers at 90°, and 40% fibers at ±45° for a lower facade.

In an optimum manner, the shearing stress Tau (t) which is applied tothe face panel must be absorbed by the fibers 100 which are oriented at+45° and −45° on each of the two skins of the structure, as illustratedin FIG. 3.

It is in fact in these conditions that the mechanical functioning of thestructure is optimized, and thus consequently its weight and cost.

However at the panels of the faces, the presence of bay angles leads tocutting of the fibers.

In a configuration of this type, the shearing stresses pass via theresin, which results in a need for an excess thickness of the skins ofthe sandwich panel in the area between bays (pier glass) in order tomake the shearing stress drop below the level permissible for the resin.For information, the permissible plane shearing stress for the resin(stack at +45° and −45° with all the fibers cut) is approximately 30 MPawhereas it is 500 MPa in the direction of the fiber when it is subjectedto compression stress. Cutting of the fibers also makes the structurefar more sensitive to environmental conditions and fatigue. Underfatigue loads, the permissible plane shearing stress for the resin isassessed as approximately 10 MPa, whereas it can be assumed that thereis resistance of more than 200 MPa in the direction of the fiber.

This leads once again to a need for excess thicknesses, otherwise therewill be a risk of weakening of the structure in the long term.

The solution proposed schematized in FIG. 7, in which the windows with alarge height comprise an octagonal profile, for which the lateral sidesare provided with a convex profile with three segments, i.e. an uppersegment at 45°, an intermediate vertical segment, and a lower segment at45°, consists of modifying the geometry of the bays such that a certainsection of fibers 100 oriented at +45° and −45° can be continuousbetween the high part and the low part of the face, and thus transferthe shearing stresses. This therefore provides a configuration which isreminiscent of that of the hatches described in U.S Publication No.US2012/0223187A1, but which differs from it in the large surface area ofthe windows and the fact that their large side is according to the axisof the car. This makes it possible to increase the cross-section ofworking fibers, without decreasing significantly the surface area ofwindows.

Since the car is subjected to low pressures, the optimum orientation ofthe fibers is approximately ±45°, and not approximately 70° as for anaircraft fuselage.

One question concerns the optimization of the angle of cutting of thebays (for a spacing imposed), in order to maximize the glazed surface.In fact, for a given spacing between bays, this cutting angle affectsdirectly the cross-section of working fibers.

Simulation by means of analytical calculation was carried out in orderto evaluate the stresses in the direction of the thread in the plies at±45°, and the plane shearing stresses in the plies at 0/90° according tothe cutting angle of the windows 20 in accordance with the configurationin FIG. 9A, in which the small sides of the window have a profile in theform of a convex “V”.

This simulation, the parameters of which show that the angle of cuttingat 45° is clearly optimum, makes it possible to determine that thisangle could be taken to 50° with at least one carbon ply at ±45°, andthat an angle of 60° can also be acceptable with the criteria retained,but with two carbon plies at ±45°.

The stacking of the composite panel (draping at 0°, +45°, −45° and 90°)corresponds to that which has been defined in order to comply with themechanical requirements in the main area of the body. For a bayconfiguration corresponding to the body concerned (L_pier glass=384 mmand H_bay=620 mm), the angle α of cutting of the bay is varied.Consequently the length “L_uncut_fiber” decreases from a maximum valuewhen α=45°, down to a zero value for a certain value of α (approximately70° in the case in question).

The results of the analysis are given in FIGS. 9B and 9C.

This analysis shows that, when the angle of the bay is greater than 70°,all the fibers at ±45° are cut, and the shearing stress in the plies at0° and 90° is greater than the permissible value, point P in FIG. 9B.Consequently, a reinforcement should be used in the area of the pierglass (increase the thickness by +250% in the case concerned), with animpact on the weight and the cost.

This analysis also shows that the cutting angle at 45° is clearlyoptimum, since the shearing flow is correctly absorbed by the fibers at+45° and −45° which are not cut, as shown in FIG. 9B, whereas the planeshearing stress is also lower than the permissible value, see FIG. 9C.

The analysis also shows that the angle of the bays could be opened up toapproximately 55° without requiring reinforcements.

FIG. 8 represents the complete body of the car with the roof 35, thedoor openings 23 and its frame 25, service openings 22, 26 such as forair-conditioning, and their frames 24, 27, as well as the end frames 28on which the walls 2 are secured.

The self-rigidified body can be assembled directly to a support chassisof the bogies of the car.

The presently disclosed embodiment can be used for all types of railwaytransport vehicles which are designed for passenger transport.

What is claimed is:
 1. A rolling vehicle car comprising lateral wallseach in a single piece formed by a sandwich composite panel made of asingle part provided with a first skin on the outer side of the car, asecond skin on the inner side of the car, and a closed-cell foam orhoneycomb core between said skins, said walls being provided with windowopenings formed by interruptions of draping of longitudinal fibers,transverse fibers and crossed diagonal fibers forming said skins, saidopenings having a polygonal form which reduces the surface of diagonalfibers interrupted in the corners of the openings, said walls formingthe faces of the car.
 2. The car as claimed in claim 1, wherein theopenings have a generally hexagonal or octagonal form comprising twolarge horizontal sides connected by convex lateral borders.
 3. The caras claimed in claim 1, wherein the openings are equipped with areinforcement border provided with a tubular frame.
 4. The car asclaimed in claim 3, wherein the reinforcement border comprises an innerwing for securing of the border on the edge of the opening on the innerside of the wall.
 5. The car as claimed in claim 4, wherein the tubularframe has a rectangular cross-section, with the inner wing extending aface of the tubular frame on the interior of the wall.
 6. The car asclaimed in claim 5, wherein the inner wing is secured on the interior ofthe wall by means of screws, rivets or other securing means.
 7. The caras claimed in claim 3, wherein a face of the tubular frame which facestowards the interior of the car is secured by means of screws, rivets orother securing means on a rim of the opening formed by the second skinprojecting from the core of the wall.
 8. The car as claimed in claim 3,wherein the reinforcement border comprises an inner collar whichreceives a fastening of a window.
 9. The car as claimed in claim 1,wherein at least one of the two skins of the sandwich structure isproduced by means of plies oriented in four preferred directions, i.e.0° (longitudinal axis of the body), 90°, +45° and −45°.
 10. The car asclaimed in claim 9, wherein the plies are plies impregnated with unitgsm substance of between 125 g/m² and 500 g/m².
 11. The car as claimedin claim 1, wherein the angle segments of said openings are inclinedbetween 45° and 60° relative to a longitudinal direction of the wall,and are preferably inclined between 45° and 50° relative to alongitudinal direction of the wall.
 12. The car as claimed in claim 9,wherein the threads at 45° are in the form of at least two ±45° pliesmade of carbon fiber.
 13. The car as claimed in claim 1, wherein thecore of the sandwich is made of material selected from amongstpolyethylene terephthalate, polymethacrylimide polyetherimide, analuminum honeycomb or a poly(m-phenyleneisophthalamide) honeycomb(structure impregnated with phenolic resin).